End-shield assemblies for grid magnetrons



April 14,1959 Ab? RUE 2, 2, END-SHIELD ASSEMBLIES FOR GRID MAGNETRONS Filed Aug. 4, 1955 I 2 Sheets-Sheet 1 IN VENTOIZ ALBERT D. LA/QUE A TTORNE'V April 14, .1959 r A. D. LA RUE- 2,382,448 v END-SHIELD ASSEMBLIES FOR GRID MAGNETRONS Filed Aug. 4, 1955 v 2 Sheets-Sheet 2 Fla. 2

/NVEN7'O/? ALBERT D. LA RUE n ted t t Pa END-SHIELD ASSEMBLIES aoR GRID MAGNETRONS Albert D. La Rue, Lexington, Mass., assignor to Raytheon Manufacturing Company, Waltham, Mass., a corporation of Delaware Application August 4, 1955, Serial No. 526,452

3 Claims. (Cl. SIS-39.63)

This invention relates generally to electron discharge devices, and more particularly to a novel end-shield assembly for a microwave generator of the magnetron type.

Magnetrons are known in which a grid structure is provided, in addition to cathode and anode struc tures, in order to influence the flow of electrons in the tube for various control purposes. In the past, these tubes have also been supplied with shielding elements or hats attached to the cathode for the purpose of eliminating undesirable leakage currents, which occur when electrons emitted from the cathode travel to the end covers or pole pieces rather than into the interaction space of the device. Since these currents contribute nothing to the operation of the tube, and, indeed, act to reduce its efficiency and in extreme cases may prevent the tube from performing its oscillating function, it is essential that they be reliably controlled. The prior art structures in which the end-shields are attached directly to the cathode have been found to be deficient in many respects, chief among which is that the end-shields often act as emitters of primary electrons which add to the leakage currents, and thus tend to defeat their purpose.

Accordingly, the present invention is directed toward a novel end-shield assembly in which the end-shields are removed from direct contact with the cathode, and made to serve as supporting elements for the grid wires. The shields are thus thermally and electrically insulated from the hot cathode, and thereby operate at a considerably lower temperature than the cathode. This construction, besides achieving a simplification of grid, end-shield, and cathode assemblies, results in a considerable reduction of leakage current from the interaction space to the end covers or poles with a consequent enhancement of the efiiciency of the tube.

The invention will be better understood as the following description proceeds, taken in conjunction with the accompanying drawings wherein:

Fig. 1 is an enlarged-scale longitudinal sectional view of an electron discharge device embodying the invention; and

Fig. 2 is a transverse sectional view along line 22 of Fig. 1.

Referring now to the drawings, and more particularly to Fig. 1 thereof, the numeral designates an electrically conductive block-like body, preferably of copper, centrally apertured to provide space for the subsequent insertion of a plurality of radially-disposed vanes 11 constituting, with the surrounding body 10, the anode structure of an electron discharge device of the magnetron type. Vanes 11, brazed or otherwise integrated with block 10, have their inner edges disposed in spaced circular array about the emissive portion 12 of the centrallypositioned tubular rod 13 constituting the cathode structure of the magnetron.

The central aperture of block 10 is enclosed at each end by appropriate end covers 14 and 15 secured to block 10 in any suitable manner, as by soldering. Each of 2,882,448 Patented; Aim-.14;

the covers; 14: and 15 has, respectively; attached thereto a. pole piece: 16. and 17 of magnetic material, which serve. in conjunction with a magnet; (not shown); to" provide: a: substantially constant intensityv magnetic: field parallel tothe axis; ofthe: tube. As: is; well known; in the art, the magnet is preferably of permanent; magnetic. compo.- sition and of horse-shoe contour, with its two extremities lying in juxtaposed relation to the polar pieces 16 and 17.

Cathode rod 13 extends through pole piece 17, and is connected to a lead-in wire 24. Rod 13 is provided with an inner conductor 26, which serves as a second lead-in wire, and which is centered within rod 13 by conventional means. Conductor 26 serves to supply current to the conventional cathode heater coil within rod 13.

Extending through the opposite pole piece 16 is a grid lead-in connection 27, which may be a tubular rod similar to rod 13. In accordance with the invention, the grid structure comprises a pair of shielding elements or plates 28 and 29 to which are secured a plurality of grid wires 30. As shown in Fig. 1, the usual end shields have been eliminated from the ends of cathode 12, and end-wise emission of electrons therefrom toward end covers 14 and 15 is effectively shielded by conductive plates 28 and 29, which also serve as support members for grid wires 30. Grid wires 30 are positioned back somewhat from the cavity openings facing the cathode so that in normal operation of the magnetron, the grid potential is more negative than that of the cathode. End shields 28 and 29 are also at a potential which is more negative than the cathode, and thus confine space charge currents to the interaction space where they may perform a useful function. It should be noted that end shields 28 and 29 are thermally and electrically isolated from cathode 12 with the result that operation is obtained at a much lower temperature than in prior devices of this type, thereby eliminating the possibility of primary electron emission from the shields themselves, which emission constituted an undesirable leakage current. The cathode structure is, of course, greatly simplified by the removal of the endshields, which, in the past, had often been designed to be reentrant in an effort to control end-shield temperature. It should also be noted that the construction of the present invention allows the end-shields to be made as large as desired without regard to mechanical problems involved in getting the cathode into place in the magnetron.

Although there has been described what is considered to be a preferred embodiment of the present invention, various adaptations and modifications thereof may be made without departing from the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. In an electron discharge device, an electron-emitting cathode, an anode structure spaced from said cathode, said anode structure including a plurality of radially disposed vanes defining a plurality of cavity resonators, cathode shielding means adjacent to but spaced from said cathode, and means for modulating the output of said device comprising a plurality of grid wires secured to said shielding means and extending through said anode structure at portions nearest to said cathode.

2. In an electron discharge device, an electron-emitting cathode, an anode structure spaced from said cathode, said anode structure including a plurality of radially disposed vanes defining a plurality of cavity resonators, shielding elements positioned adjacent the ends of said cathode, and means for modulating the output of said device comprising a plurality of grid wires secured to said shielding elements and extending through said anode structure at portions nearest to said cathode.

3. In an electron discharge device, an electron-emitting cathode, an anode structure spaced from said cathode,

said anode-structureincluding a plurality of radially dis- References in the file of patent I UNITED STATES PATENTS Edelman Sept. 19, 1933 Fisk Feb. 25, 19 47 Koehler Mar. 18, 1952 Hansell Dec. 1, 1953 Haagensen May 29, 1956 Spencer Mar. 5, 1957 

